The present invention relates to a physical-biochemical process system for treating contaminated groundwater to remove volatile organic compounds (VOCs) and other objectionable volatile and nonvolatile contaminants from said groundwater. The process system of this invention represents a low cost and highly efficient alternative to present groundwater treatment technology which causes secondary air pollution.
About 70 percent of potable water in the U.S.A. is supplied by groundwater. Groundwater contamination, which is a national major concern, is about 71 percent caused by industrial accidents (chemical spills, tank leaks, etc.), 16 percent caused by railroad or truck's chemical accidents, and 13 percent caused by leachates from lagoons or dumpsites.
The primary reasons for treating groundwater are: potable use (39 percent), clean-up of aquifer to prevent spread of contamination (48 percent), and industrial and commercial use (13 percent). In any case, the potentially hazardous VOCs must be removed. Timely clean-up of aquifer to prevent spread of contamination is extremely important because the damage can be beyond repair if the spread of contamination is too wide.
Toxic organic compounds commonly found in groundwater include, but will not be limited to, the following:
______________________________________ Percent of Organic Compounds Occurr- Concentration in Groundwater ences Range ______________________________________ Carbon tetrachloride 5 130 ug/l-10 mg/l Chloroform 7 20 ug/1-3.4 mg/l Dibromochloropropane 1 2-5 mg/l DDD 1 1 ug/l DDE 1 1 ug/l DDT 1 4 ug/l CIS-1,2-dichloroethylene 11 5 ug/l-4 mg/l Dichloropentadiene 1 450 ug/l Diisopropyl ether 3 20-34 ug/l Tertiary methyl-butylether 1 33 ug/l Diisopropyl methyl phosphonate 1 1,250 ug/l 1,3-dichloropropene 1 10 ug/l Dichlorethyl ether 1 1.1 mg/l Dichloroisopropylether 1 0.8 mg/l Benzene 3 0.4-11 mg/l Acetone 1 10-100 ug/l Ethyl acrylate 1 200 mg/l Trichlorotrifloroethane 1 6 mg/l Methylene chloride 3 1-21 mg/l Phenol 3 63 mg/l Orthochlorophenol 1 100 mg/l Tetrachloroethylene 13 5 ug/l-70 mg/l Trichloroethylene 20 5 ug/l-16 mg/l 1,1,1-trichloroethane 8 60 ug/l-25 mg/l Vinylidiene chloride 3 5 ug/1-4 mg/l Toluene 1 5-7 mg/l Xylenes 4 0.2-10 mg/l EDB 1 10 ug/l Others 1 NA ______________________________________
The present technologies for groundwater treatment include: air stripping without air emission control, granular activated carbon, chemical oxidation, and biological processes. Air stripping without air emission control is not acceptable in many states. Granular activated carbon contactor is technically feasible for water purification, but may be economically unfeasible when it is used alone. Chemical oxidation is not cost-effective and may give undesirable residuals. Biological process for groundwater treatment has not been fully developed.
The present invention is an efficient and cost-effective groundwater purification system aiming at clean-up of aquifer to prevent spread of VOCs contamination. The purified groundwater is to be discharged to a recharging well. The present invention considers the affordability, performance, governmental acceptance, secondary pollution elimination and simplicity in operation.
Industrial or municipal wastewaters containing VOCs can also be efficiently treated by the process system of the present invention.